Calcium magnesium imbalance in clovers: A cause of negative yield response to liming |
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Authors: | R A Carran |
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Institution: | (1) Grassland Division, DSIR, Private Bag, Palmerston North, New Zealand |
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Abstract: | Three pot experiments, in which causes of negative yield responses to liming were investigated, are reported. The soil used,
Waimumu silt loam (Fragiochrept), differed from others that have been reported to show negative yield response to liming,
in that it is only moderately weathered and leached, only moderately acid and has previously shown positive yield responses
to liming. Deficiencies of Zn and Mg were identified, but limed (pH 6.8) soils still showed a 40% yield depression even where
all nutrients were supplied daily. Phosphorus availability was little affected by liming, and despite Mg and Zn addition,
yields were depressed at high lime (pH 6.4) and high P while plants showed leaf symptoms of Mg deficiency. Neither plant nor
soil analyses indicated low Mg levels but Ca: Mg ratios in soil were 22:1. When a pH range 5.2–6.1 was produced by liming
with CaCO3 and MgCO3 at ratios between 100:0, and 50:50 on an equivalent basis, negative yield response was eliminated at Ca:Mg of 50:50. There
was no evidence that Mg was fixed or rendered unavailable at the higher pH levels. A Ca induced Mg deficiency arising when
exchangeable Ca:Mg>20 is suggested as the cause. The role of variable surface charge in converting soils that respond positively
to lime to a negative response condition is discussed. |
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Keywords: | calcium carbonate Mg deficiency Trifolium repens Trifolium subterraneum variable surface change |
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